1. Field of the Invention
The present invention relates to detection assays, and more particularly, to the use of fluorescent moieties in proximity to metallic surfaces to change the spatial distribution of fluorescence in an angular dependent manner thereby increasing sensitivity of the assay.
2. Background of the Related Art
Over the past 10 years, fluorescence has become a dominant technology in medical testing, drug discovery, biotechnology and cellular imaging. The use of fluorescence technology has greatly enhanced the ability to detect specific molecules leading to rapid advancements in diagnostics. For example, fluorescence detection is widely used in medical testing and glucose analysis because of the high degree of sensitivity obtained using fluorescent techniques. Small numbers of molecules can be detected using fluorescence technology.
Metal-Enhanced Fluorescence (MEF), a phenomenon where the quantum yield and photostability of weakly fluorescing species are dramatically increased, due to proximity to free-electron rich metals, is becoming a powerful tool for the fluorescence-based applications of drug discovery [1, 2] high-throughput screening [3, 4] immunoassays [5] and protein-protein detection [1, 4, 6].
In this regard, many surfaces have been developed for metal-enhanced fluorescence [1-5], primarily based on silver nanoparticles, such as those comprised of silver islands [1, 5, 7], silver colloids [8], silver nano-triangles [9], silver nanorods [10] and even fractal-like silvered surfaces [11]. Several modes of silver deposition have also been developed, such as by wet chemistry [1, 9, 10], deposition by light [12] and electrochemically [13], on glass [5] and plastic substrates [14], HTS wells [3] and even electrodes [15].
However, fluorescence is normally an isotropic process, which means that when a fluorophore is excited, its fluorescence emission radiates in 360°, with an equal intensity at all angles. Thus, nearly all fluorescence is lost in many analytical and clinical applications of fluorescence because the detection measurement occurs over just a few degrees. For example, a fluorescence fluorometer, works by exciting a solution of fluorophores and measuring the fluorescence emission at 90° to the excitation light. In these measurements, only 1-5% of light, at the very best, is observed, meaning that >95% of the total light available is lost.
Providing a system and method that has the capability of capturing this light, would significantly increase detection limits in the many applications of fluorescence, such as in bio-assays and even imaging histology. Thus, there is a need for a biosensor platform and system that overcomes the shortcomings of the prior art and provides for increased sensitivity and signal production.